38 ROYAL SOCIETY OF CANADA 
ponents may be found whose ratio in the solution, or precipitate, 
changes whenever the composition of the solution, or precipitate, 
changes, and only then; and since for the interpretation of the results it 
is only necessary to know whether the composition of solutions and 
precipitates remains constant or changes from experiment to experi- 
ment, it is sufficient to plot these ratios instead of the compositions 
themselves. An illustration is afforded by the following curve taken 


2B O3°V, 0; + FH 0 
GB203 SN, 0; + 9H 0 
from Mr. Allan’s paper on the basic nitrates of bismuth. The abscissæ 
give the ratios between N,0; and H,O in the solutions, and the 
ordinates those between Bi,O, and N,0, in the precipitates. 
The Mechanism. 
Although a great deal of use has been made of the Phase Rule in 
classifying chemical reactions, and in the study of solutions and alloys, 
and more recently of such compounds as steel and the various commer- 
cial varieties of iron, comparatively little attention has been paid to 
the mechanism by means of which the results foretold by it are arrived 
at in the system. The subject is not only interesting in itself, but 
leads to an extension of the method of identifying chemical individuals 
among the basic salts, to the case where the precipitation is carried out 
by means of potash, ammonia, etc., although here the system no longer 
consists of three components only, and consequently the direct applica- 
tion of the Phase Rule in the manner just illustrated is not possible. 
AN, Ox 
005 -0/0 ‘O15 -020 O25 -030 H0 

